The embodiments of the present invention relate to a self-piercing riveting process and, more particularly, to a die member for use in a self-piercing riveting process.
In the joining of components used in high volume vehicle production, it may be desirable to use mechanical fasteners to help achieve the required strength and durability of joints. One type of mechanical fastener used in vehicle production is a self-piercing rivet (SPR).
The general principles of self-piercing rivet technology are known in the art. To apply a self-piercing rivet to workpieces to be joined, a portion of a first workpiece or panel is placed upon a bearing surface of a die member, so as to overlie a die cavity formed in the die member. Portions of one or more additional panels are then stacked on the portion of the first panel overlying the die cavity. The panels are secured in position with respect to each other and with respect to the die member, to prevent relative movement of the parts during application of the rivet. The die cavity may also contain a die post which assists in forcing a portion of the rivet to spread or deflect radially outwardly when pressure sufficient to pierce the first workpiece is applied to the rivet. The rivet also pierces surfaces of the second panel overlying the first panel. In a known manner, up to four layers of material may be joined using existing SPR processes.
During application of the rivet to the workpieces to be joined, a feature known as an SPR “button” is produced. This SPR button is in the form of a protrusion in a surface of the second panel along a side of the second panel opposite the side pierced by the rivet. One of the challenges encountered during SPR joining is the nucleation and propagation of cracks on the “button” side of the joint, along corners of the button shaped by the floor and walls of the die cavity during the SPR operation. The presence and size of these cracks can affect the quality of the joint and the viability of SPR technology as a fastening option.
Thus, a need exists for a die geometry in which crack formation in the rivet material along the SPR button during formation of the button is reduced or minimized.